DENIERS SAY:

The IPCC uses flimsy evidence to try to scare us about global warming.

SCIENCE SAYS:

If anything, the IPCC has underestimated the impacts of climate change.

Deniers love to hate the United Nations Intergovernmental Panel on Climate Change (or the “IPCC”), an international scientific body that reviews and assesses the best available climate research produced worldwide. Hundreds of independent scientists review the peer-reviewed research on climate change and summarize it in a few reports. Then hundreds more experts review their work. And then, the world’s governments go through the reports line by line. What does this mean? It means the end product is a consensus document —or in other words, it generally underestimates what will happen to the Earth’s climate.

Further, fossil fuel emissions are currently close to the "worst-case" IPCC projections. Arctic sea ice is declining much faster than the IPCC predicted. Indeed, in many cases, IPCC projections have underestimated the speed and intensity of observed climate change.

Additional info from the Union of Concerned Scientists

One critical strategy the IPCC uses to ensure the scientific credibility and political legitimacy of its reports is to represent the range of scientific opinion on climate change fairly. To this end, the IPCC provides several channels for input from experts along the entire spectrum of opinion, even global warming contrarians.

First, accredited NGOs from all sides of the issue are welcome as observers at the opening plenary session and some other sessions over the course of the report production cycle. In addition, well-known contrarians can and do become contributing authors by submitting material to lead authors, and play advisory roles for their governments by working with government representatives to revise and approve the final SPMs.

The presence of climate change experts from industry and environmental organizations in the assessment process also illustrates the IPCC’s desire to seek input from outside traditional research institutions. Industry examples have included representatives from the Electric Power Research Institute and ExxonMobil. Environmental examples have included representatives from Environmental Defense, the Natural Resources Defense Council, and others all over the world.

Given the many stages at which experts from across the political and scientific spectrum are included in the process, it is difficult to accept the contrarian claim that the IPCC produces biased reports (PDF).